Characterization of purinergic receptor-evoked increases in intracellular Ca2+ transients in isolated human and rodent insulin-secreting cells

In vivo many factors determine the regulation of insulin secretion from the ?-cells of the pancreatic islets of Langerhans. The most predominant influence is a rise in the concentration of plasma glucose, which will promote secretion by mechanisms associated with Ca2+ influx across the plasma membrane. Insulin release is also governed by changes in the concentration of circulating amino acids, gastrointestinal hormones, neuropeptides and neurotransmitters. These influences are important avenues for ?-cell regulation as they not only provide a link between the gastrointestinal tract and the pancreatic islets — the enteroinsular axis, but they also govern the neurohormonal control of secretion. For many years it has been recognised that extracellular ATP is a potent insulin secretagogue. In vitro it has been demonstrated using rodent and clonal insulin-secreting cells that purinergic receptor activation is coupled to an increase in [Ca2+]i. However, few studies have examined intracellular Ca2+ signalling in isolated human insulin-secreting cells. In a recent paper we have shown that ATP and other agonists of the purinergic receptor evoke marked increases in [Ca2+]i in ?-cells isolated from transplantable human islets of Langerhans. In this paper we examine: (i) the purinergic receptor subtype present in human tissue, (ii) compare purinergic receptor-evoked increases in [Ca2+]i in both rodent and human ?-cells and (iii) demonstrate that intracellular Ca2+ signals can also be recorded in cryopreserved human ?-cells originally isolated from cadaver organ donors.</p

ATP-induced intracellular Ca2+ signals in isolated human insulin-secreting cells

Using isolated ?-cells from human islets of Langerhans we have demonstrated that purinergic receptor agonists are functionally coupled to rises in the intracellular calcium ion concentration (Ca2+i). The effects of ATP, ADP and AMP have been examined over a range of concentrations, 0.5 to 500?M. The actions of ATP were more potent than those of either ADP or AMP suggesting that a P2-type of purinergic receptor operates in these cells. Responses to ATP were concentration-related, but exhibited marked desensitisation at high concentrations (>100?M). Purinergic receptor agonists elevate Ca2+i by mechanisms that involve both Ca2+ influx and Ca2+ mobilisation from intracellular stores. The physiological significance of our data has been discussed, and related to previous studies carried out upon rodent and clonal insulin-secreting cells. © 1994 Springer-Verlag.</p

Dietary fat in relation to fatty acid composition of red cells and adipose tissue in colorectal cancer

Fatty acids were determined in erthrocytes in 49 patients with colorectal cancer and compared with age and sex-matched controls. Marginally increased levels of stearic acid (P = 0.057) and oleic acid (P = 0.064) and decreased arachidonic acid (P = 0.043) occurred in cancer patients. There was no difference in the stearic to oleic acid ratio between the two groups. Dietary intake, assessed by dietary recall and adipose tissue analysis was also not different. In control subjects the polyunsaturated:saturated (P:S) fatty acid ratio correlated between diet and adipose tissue (P less than 0.01, at least). In contrast cancer patients showed different correlations; in particular dietary and erythrocyte P:S fatty acid ratios correlated (P less than 0.01). These findings may indicate disturbed fat metabolism in cancer patients. The erythrocyte stearic to oleic acid ratio is of no diagnostic value

Dietary fat in relation to fatty acid composition of red cells and adipose tissue in colorectal cancer

Fatty acids were determined in erthrocytes in 49 patients with colorectal cancer and compared with age and sex-matched controls. Marginally increased levels of stearic acid (P = 0.057) and oleic acid (P = 0.064) and decreased arachidonic acid (P = 0.043) occurred in cancer patients. There was no difference in the stearic to oleic acid ratio between the two groups. Dietary intake, assessed by dietary recall and adipose tissue analysis was also not different. In control subjects the polyunsaturated:saturated (P:S) fatty acid ratio correlated between diet and adipose tissue (P less than 0.01, at least). In contrast cancer patients showed different correlations; in particular dietary and erythrocyte P:S fatty acid ratios correlated (P less than 0.01). These findings may indicate disturbed fat metabolism in cancer patients. The erythrocyte stearic to oleic acid ratio is of no diagnostic value

Loss of functional K(ATP) channels in pancreatic ?-cells causes persistent hyperinsulinemic hypoglycemia of infancy

Persistent hyperinsulinemic hypoglycemia of infancy (PHHI) is a disorder of childhood associated with inappropriate hypersecretion of insulin by the pancreas. The pathogenesis of the condition has hitherto remained controversial. We show here that insulin-secreting cells from a homogeneous group of five infants with PHHI lack ATP-sensitive K+ channel (K(ATP)) activity. As a consequence, PHHI ?-cells are spontaneously electrically active with high basal cytosolic Ca2+ concentrations due to Ca2+ influx. Our findings define the pathogenesis of this disease as a novel K+ channel disorder.</p

Ionic control of ? cell function in nesidioblastosis. A possible therapeutic role for calcium channel blockade

A preterm female infant presented with intractable hypoglycaemia within 10 minutes of delivery. Normoglycaemia could be maintained only by the intravenous infusion of glucose at a rate of 20-22 mg/kg/min. Persistent hyperinsulinaemic hypoglycaemia of infancy was diagnosed from an inappropriately raised plasma insulin concentration (33 mU/l) at the time of hypoglycaemia (blood glucose <0.5 mmol/l). Medical treatment with glucagon, somatostatin, and diazoxide led to only a modest reduction in the intravenous glucose requirement; a 95 pancreatectomy was performed and histological 'nesidioblastosis' confirmed. In vitro electrophysiological studies using patch clamp techniques on isolated pancreatic ? cells characterised the ionic basis for insulin secretion in nesidioblastosis. The ? cells were depolarised in low ambient glucose concentrations with persistently firing action potentials; these were blocked reversibly by the calcium channel blocking agent verapamil. Persistent postoperative hyperinsulinaemic hypoglycaemia was treated with oral nifedipine. This increased median blood glucose concentrations from 3.5 to 4.8 mmol/l and increased in duration the child's tolerance to fasting from 3 to 10.5 hours. These data allude to an abnormality in the ionic control of insulin release in nesidioblastosis and offer a new logical approach to treatment which requires further evaluation.</p